Ultrasonic array transducers comprise a plurality of transducer elements that are used to transmit and receive ultrasonic energy to generate an image of a target. Each transducer element operates as an independent point source. Generally, the greater the quantity of transducer elements, the greater the quality of the image. Each of these individual transducer elements must be electrically connected to a cable, which is then connected to an ultrasound system. The electrical connection between the individual transducer elements and the cable is typically made using a wire.
In a typical ultrasound array transducer, the transducer elements are out of plane with the cable. As a result, the wires that electrically connect the cable and the transducer elements must be bent 90 degrees to allow connection to the cable. However, making such a bend is difficult to achieve in a straight transducer array and even more difficult in curved transducer arrays because of the lack of strength of the connection between the wire and the transducer elements. Typical connection methods include ultrasonic bonding and wedge bonding. Bonds formed by such methods are weak, and they do not have the strength to withstand the force imposed by when bending the wire 90 degrees. Consequently, the bonds will fail when subjected to the bending force, causing the wires to become disconnected from the transducer elements.
To avoid this problem, the wires are connected to the transducer elements either by hand soldering ribbon wire or by using flexible circuits that rely on mechanical pressure to make electrical contact. Each of these methods has disadvantages. With respect to hand soldering, the heat generated in the process tends to depolarize the piezoelectric ceramic material of the transducer elements, thereby adversely affecting the performance of the transducer (i.e., low and non-uniform signals). On the other hand, the use of a flexible circuit results in several additional layers being placed between the piezoelectric ceramic material of the transducer elements and a backing material. Because the flexible circuit is located within the acoustic path, it can interfere with acoustic performance of the transducer.
Thus, there is a need for a method of making an ultrasonic array transducer that can minimize such concerns.